1. Field of the Invention
The present invention relates to a battery including a spirally wound electrode body in which a cathode and an anode are layered with a separator in between and spirally wound.
2. Description of the Related Art
In recent years, many portable electronic devices such as a combination camera (Videotape Recorder), a mobile phone, and a notebook personal computer have been introduced. As a power source for such portable electronic devices, development of a small and light-weight battery having the high energy density, in particular the secondary battery has been strongly demanded. As a secondary battery to meet such a demand, for example, a lithium secondary battery using lithium as an electrode reactant has been practically used. However, as the mobile devices have been sophisticated in these years, the higher capacity thereof has been demanded.
As a method to realize the high capacity, for example, the amount of the active material filled in the battery may be increased. For example, in a lithium secondary battery having a structure in which a cathode and an anode provided with an active material layer on the both faces of the current collector are layered with a separator in between and spirally wound, when the thickness of the active material layer is increased, the ratio of the current collector and the separator in the battery is decreased, the filling amount of the active material is increased, and thus the capacity can be improved. However, when the thickness of the active material layer is increased, there is a disadvantage that cracks and breaks are easily generated in the active material layer when the lamination is spirally wound. Therefore, for example, it is proposed that the stress is relaxed by, for example, setting the thickness of the active material layer on the spirally-winding inner face side smaller than that of the active material layer on the spirally-winding outer face side (for example, refer to Japanese Unexamined Patent Application Publication No. 8-130035).